32 /* * Structure for installing or delivering an upcall if the * measured bandwidth is above or below a threshold. * * User programs (e.g. daemons) may have a need to know when the * bandwidth used by some data flow is above or below some threshold. * This interface allows the userland to specify the threshold (in * bytes and/or packets) and the measurement interval. Flows are * all packet with the same source and destination IP address. * At the moment the code is only used for multicast destinations * but there is nothing that prevents its use for unicast. * * The measurement interval cannot be shorter than some Tmin (currently, 3s). * The threshold is set in packets and/or bytes per_interval. * * Measurement works as follows: * * For >= measurements: * The first packet marks the start of a measurement interval. * During an interval we count packets and bytes, and when we * pass the threshold we deliver an upcall and we are done. * The first packet after the end of the interval resets the * count and restarts the measurement. * * For <= measurement: * We start a timer to fire at the end of the interval, and * then for each incoming packet we count packets and bytes. * When the timer fires, we compare the value with the threshold, * schedule an upcall if we are below, and restart the measurement * (reschedule timer and zero counters). */